This series and parallel sensor circuit was found in Popular Electronics from the 1990s. Any SCR can be used and the supply voltage depends on the load.
This 2004 circuit is based on the ionization effect that occurs in old incandescent lamps with...
This bidirectional current sensing circuit was found in a 2005 Linear Technology application manual....
This circuit can be used in decoration or to draw attention, in a “fake” assembly for example. What he...